Integrated Services Digital Network (ISDN) standard has been developed to enable multiple digital channels to be operated simultaneously through existing analog phone lines thereby advantageously increasing their bandwidth. Through the ISDN interface, multiple devices, such as telephone, fax, computer, video conferencing and routers, can share a single line. Information from the various devices can be routed to the proper destination. Generally, ISDN devices transceive information in 8 kHz frames.
An ISDN-oriented modular (IOM-2) bus is an ISDN-based bus. The IOM-2 bus is described in, for example, ICs for communications, IOM-2 Interface Reference Guide, Infineon Technologies, which is herein incorporated by reference for all purposes. The IOM-2 bus provides a symmetrical full-duplex communication link and divides an ISDN frame into 8-bit slots, referred to as “octets” or “timeslots”. Two operating modes are available in the IOM-2 interface. The first mode is terminal mode (TE) and the second is the line card mode (LT). In the TE mode, an ISDN frame has 12 octets while 32 octets are provided in the LE mode.
Since IOM-2 devices handle ISDN data, communication is through 2 B-channels for data transfer and 1 D-channel for control signals. These channels are time-multiplexed over a four-wire serial interface. Data is carried over data upstream (DU) and data downstream (DD) signals. Due to the fact that the IOM-2 standard uses the common B- and D-channels for data transmission, only three timeslots (slots) are accessed during an ISDN frame. However, with the availability of high-speed transfer devices, such as Universal Serial Bus (USB) or Ethernet, and the desire to provide integrated services (e.g., voice, data, video), the current bandwidth of the IOM-2 interface is not sufficient.
From the foregoing discussion, it is desirable to increase the bandwidth of existing ISDN-based interfaces.